The present invention relates to polysiloxanes, methods for producing such polysiloxanes and high refractive index silicone materials made from such polysiloxanes, for example, for use in intraocular lenses. More particularly, the invention relates to polysiloxanes which are structured and are produced to provide silicone materials which have an advantageous combination of properties, including a high refractive index, and are useful in intraocular lenses.
Intraocular lenses (IOLs) have been known for a long time. Such lenses are surgically implanted into the human eye to replace damaged or diseased lenses of the eye.
Whereas IOLs can be made from "hard" polymeric or glass optical materials, soft resilient polymeric materials comprising polysiloxane polymers or copolymers have been increasingly used in the art for this purpose.
IOLs made from silicone polymeric materials are preferably deformable, so that for implantation a smaller incision needs to be surgically cut in the eye than for the implantation of "hard" IOLs. In this respect, the size and mechanical characteristics of the silicone polymeric IOLs play an important role. As it will be well understood by those skilled in the art, for successful implantation the lens must have sufficient structural integrity, elasticity and elongation and small enough size to permit the folding for insertion through a small incision. After insertion, the lens must, of course, regain its original molded shape and have sufficient structural integrity to retain such shape under normal use conditions.
It will be further understood by those skilled in the art that the thinner is the lens, the easier is the surgical insertion procedure. On the other hand, in order to function as an IOL, the lens material must have sufficient optical refractory power. Consequently, the higher is the optical refractive index of the silicone material, the thinner can be the lens to obtain the same optical refractory power.
Some silicone polymeric materials described in the prior art contain a reinforcer distributed in the polymeric silicone resin. Usually such reinforcement of the silicone polymeric material is necessary for the polymeric material to attain adequate structural strength to be used as a foldable IOL. Examples of reinforced silicone resins suitable for use as soft contact lenses or IOLs are described in U.S. Pat. Nos. 3,996,187; 4,615,702; 3,996,189.
Travnicek U.S. Pat. No. 3,996,189 discloses that the inclusion of diphenyl siloxane or phenyl-methyl siloxane into a polysiloxane increases the refractive index of the polymer. However, using such phenyl-containing siloxanes as refractive index increasing components results in a polymer which has reduced flexibility or elongation. Thus, although the refractive index is advantageously increased, the elongation of the polymer (and the foldability of an IOL produced from such polymer) is disadvantageously decreased. It would be advantageous to provide a siloxane polymer with high refractive index and sufficient elongation to provide a foldable IOL.
Koziol et al U.S. Pat. No. 4,615,702 discloses IOLs made from silicone polymers obtained by polymerization of such monomers as octamethylcyclotetrasiloxane, octaphenylcyclotetrasiloxane, trimethyltriphenylcyclotrisiloxane, and divinyltetramethyldisiloxane. Although such IOLs may have high refractive indexes because of the relatively high concentrations of phenyl groups, they also disadvantageously have reduced elongation, as do the materials disclosed by Travnicek U.S. Pat. No. 3,996,189, noted above.
Canadian Patent 1,273,144 discloses the inclusion of refractive index modifying groups, such as phenyl groups, into hydride-containing siloxanes by reacting a portion of the hydride groups with carbon-carbon unsaturation bonded to the refractive index modifying group. After this reaction, the unreacted hydride groups of the modified hydride-containing siloxane are reacted with a compound having at least two carbon-carbon unsaturated bonds to form a cross-linked polysiloxane. This system is somewhat difficult to control and may not be suitable for mass production of silicone lenses because of potentially large batch-to-batch quality variations. For example, the refractive index modifying groups should be sufficiently numerous and evenly distributed in the hydride-containing siloxane to provide the desired refractive index without detrimentally affecting the other properties of the final polymer. At the same time, the unreacted hydride groups remaining on the siloxane must be sufficiently numerous and evenly distributed to provide for the desired cross-linking reaction. These factors can create a reaction control problem which may result in a final polymer not having the desired refractive index and/or not having one or more other desired physical properties. It would be advantageous to provide for increasing the refractive index of a polymer with little or no effect on the cross-linking of the final polymer.
Mbah U.S. Pat. No. 4,882,398 discloses the presence of up to about 40% by weight of a resinous organo-siloxane copolymer consisting essentially of trimethyl siloxy, dimethyl vinyl siloxy and SiO.sub.2 units in a diorgano vinyl siloxy-terminated polydiorgano siloxane containing at least 95 mole % of dimethyl siloxane units and having a viscosity greater than about 12 Pa.s at 25.degree. C. decreases the viscosity of the mixture relative to the viscosity of the polydiorgano siloxane. Although this patent does disclose certain aryl and aralkyl groups attached or bonded to a siloxane, there is no teaching or suggestion of any effect on the refractive index of the final polymer as a result of the inclusion of the monovalent hydrocarbon radicals or monovalent halogenated hydrocarbon radicals. Also, the amount of these groups which is included is such as to have little or no effect on the refractive index of the final polymer.